To improve the cold start behavior of internal combustion engines, a possible utilization of the exhaust gas heat has long since been known from the prior art. During the cold start phase the exhaust gas heat is transmitted to the cooling medium of a cooling circuit by using a heat exchanger in order to achieve a rather fast and uniform heating of the individual engine components via the cooling circuit. As such, the desired operating temperature can be reached faster and in addition the component wear, the fuel consumption and the pollutant emission until reaching the operating temperature can be reduced distinctly.
After reaching the operating temperature, a further heating of the cooling circuit by the exhaust gas stream, however, is undesired, in order to avoid overheating of the cooling circuit. Therefore, a switchable bypass system with at least two exhaust gas flow ducts connected in parallel usually exists in the region of the heat exchanger. The expenditure for the regulation and/or control, and for the usually electromotive actuation of such bypass system, is enormous in particular in view of the relatively short utilization during the cold start phase as seen over the entire operating period.
In EP 1 852 585 A1 a bypass system for internal combustion engines is described, which includes a considerably simplified control and actuation. The exhaust gas stream is regulated using an exhaust gas flap which is acted upon by a spring and can be actuated by a temperature-operated actuator with a thermocouple.
In conjunction with the global discussion on climate, increasingly stricter regulations with respect to energy efficiency and CO2 emission of internal combustion engines are to be expected in the future. To deal with this problem, efforts have recently been made to utilize the exhaust gas heat of internal combustion engines during the entire engine operation, if possible, and preferably convert the same into electric energy, with which accumulators can be charged or electrical appliances can be operated. From the prior art, so-called “thermoelectric generator modules” (in the following: TEG modules) are already known, which convert thermal energy into electric energy. At present, however, in some operating conditions of the internal combustion engines the maximum exhaust gas temperature distinctly lies above the maximum admissible temperature with which the TEG modules may be acted upon. To avoid a destruction of the TEG modules due to overheating, complex and expensive protection measures therefore are required.
Therefore, it is important to create a device for exhaust gas heat utilization using TEG modules, in which the modules used are reliably protected against thermal overload with minimum effort.